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The management of parapneumonic effusions and empyema
Richard W. Light
parapneumonic, empyema, Effusion, pneumonia
Editorial.

It is estimated that four million patients develop bacterial pneumonia in the United States annually and approximately 20% of these require hospitalization1. The incidence of parapneumonic effusion in patients hospitalized with pneumonia is about 40%2. Patients who have pneumonia and pleural effusion have greater morbidity and higher mortality rates than do patients with pneumonia alone3. In one study, the relative risk of mortality in patients with community-acquired pneumonia was 7.0 times higher for patients with bilateral pleural effusions and 3.4 times higher for patients with a unilateral pleural effusion of moderate or greater size compared with other patients with community-acquired pneumonia alone3. Improper management of the parapneumonic pleural effusion is at least partially responsible for some of the increased morbidity and mortality.

One reason for the increased morbidity and mortality seen in pneumonia patients with effusions is that the presence of a pleural effusion is associated with a more advanced pneumonia. In one study the prevalence of pleural effusion was 40% in bacteremic patients and 21% in nonbacteremic patients4. The presence of a pleural effusion greater than 1.0 cm in thickness on a decubitus chest radiograph has served as a definite criterion for admission to the hospital in some studies5.

DEFINITIONS

A parapneumonic pleural effusion is a pleural effusion associated with bacterial pneumonia, lung abscess or bronchiectasis6. An empyema is pus in the pleural space. By definition pus is thick, purulent-appearing pleural fluid. A complicated parapneumonic effusion is a parapneumonic effusion for which tube thoracostomy is necessary for its resolution. A loculated parapneumonic effusion is a parapneumonic effusion which is not free-flowing. A multi-loculated parapneumonic effusion is a loculated parapneumonic effusion with more than one loculus.

 

NATURAL HISTORY OF PARAPNEUMONIC EFFUSION

The evolution of a simple parapneumonic effusion to an empyema represents a continuous progression from a small amount of free-flowing, non-infected pleural fluid to a large amount of frank pus which is multi-loculated and is associated with a thick visceral pleura that prevents the underlying lung from expanding if the fluid is removed. When a patient develops pneumonia, the rate of pleural fluid formation is increased. Mainly, the increase is due to lung interstitial fluid, secondary to the pneumonia, traversing the visceral pleura to enter the pleural space. Increased permeability of the capillaries in the pleurae probably also contributes to the increased rate of fluid formation. When the amount of pleural fluid entering the pleural space exceeds the capacity of the pleural lymphatics to reabsorb the fluid, pleural fluid begins to accumulate. When the fluid initially begins to accumulate, the effusion is not loculated. The pleural fluid has a normal glucose and pH and the lactic acid dehydrogenase (LDH) level and the WBC count are low7. In some patients the process progresses with bacteria invading the pleural fluid. After the pleural fluid becomes infected, the pleural fluid glucose and pH become progressively lower, the LDH becomes progressively higher and the fluid becomes increasingly more viscid. In addition, sheets of fibrin form that partition the fluid into loculi and cover the visceral pleura which prevents the underlying lung from re-expanding.

CLASSIFICATION OF PARAPNEUMONIC EFFUSION AND EMPYEMA

The American College of Chest Physicians has recently developed a new classification of parapneumonic effusions and empyema which is based upon the radiologic characteristics of the effusion, the pleural fluid bacteriology and the pleural fluid chemistry (Table 1)8. It is modeled somewhat after the TNM system for staging cancer. The key aspects to note about this classification are the characteristics that indicate that the patient has a moderate to high risk of a poor outcome without drainage. Radiological characteristics associated with a poor prognosis are an effusion that occupies more than 50% of the hemithorax, is loculated, or is associated with a thickened parietal pleura. However, I personally would not use the thickened parietal pleura as a sign of a poor prognosis. In a recent study of 50 patients with parapneumonic effusions, 46 of 50 (92%) had pleural thickening. The thickness of the pleura, however, was not related to the requirement for surgery9. Bacteriological criteria associated with a poor prognosis are a positive culture, a positive Gram stain, or the presence of pus. The pleural fluid chemistry criterion associated with a poor prognosis is a pleural fluid pH less than 7.20. If the pleural fluid pH is used, it is important to measure the pH with a blood gas machine; pH meters and dip sticks do not provide sufficiently accurate pH measurements10. Alternative pleural fluid chemistry criteria are a pleural fluid glucose less than 60 ml/dl8 or a pleural fluid LDH more than three times the upper limit of normal for serum2.

TREATMENT OF PARAPNEUMONIC EFFUSION AND EMPYEMA

Antibiotics: Antibiotic therapy is indicated for patients with parapneumonic effusions or empyema. The initial antibiotic selection should be based on whether the pneumonia is community- or hospital-acquired and the severity of illness. Pleural fluid antibiotic levels are comparable to those in serum7, except for aminoglycosides which appear to penetrate poorly into purulent pleural fluid. The recommended treatment for a patient with community-acquired pneumonia that is not severe is a β-lactam-β-lactamase inhibitor with or without a macrolide11. Alternatively, the newer generation fluoroquinolones such as levofloxacin can be used. The recommended treatment for severe community-acquired pneumonia is a macrolide or a new generation fluoroquinolone plus cefotaxime, ceftriaxone, or a β-lactam-β-lactamase inhibitor11. Pneumonia acquired in institutions such as nursing homes or hospitals is frequently caused by enteric gram-negative bacilli, P. aeruginosa, or S. aureus with or without oral anaerobes. If S. Aureus infection is suspected, either nafcillin or vancomycin should be administered. If gram-negative infection is suspected, the patient should be treated with a third generation cephalosporin or a β-lactam-β-lactamase inhibitor plus an aminoglycoside.

Initial Therapeutic Thoracentesis. When a patient with pneumonia is first evaluated, the possibility of a parapneumonic effusion should be considered. If both diaphragms cannot be seen throughout their entirety on both the posteroanterior and lateral chest radiographs, then bilateral decubitus chest radiographs, chest ultrasound or a chest CT scan should be obtained. If the thickness of the pleural fluid is less than 10 mm, the effusion is non-significant and no thoracentesis is indicated2. If it appears from the standard radiographs that the patient has a loculated pleural effusion, this possibility should be evaluated with ultrasound.

If the thickness of the pleural fluid is more than 10 mm or if the pleural fluid is loculated, one needs to examine the pleural fluid to determine the category of the effusion. Since a thoracentesis is required for this examination, it is reasonable to perform a therapeutic rather than a diagnostic thoracentesis. If the fluid is removed completely with the therapeutic thoracentesis and does not reaccumulate, no additional therapy needs to be directed toward the effusion. At the time of the initial therapeutic thoracentesis, the pleural fluid should be Gram-stained and cultured and analyzed for the cell count and differential, LDH, glucose and pH levels. Indicators of a poor prognosis from the pleural fluid include a positive Gram-stain or culture, a glucose less than 60 mg/dl, an LDH more than three times the upper limit of normal, or a pH less than 7.20 (Table 2).

If the therapeutic thoracentesis removes all the pleural fluid and the fluid recurs, the next step is guided by the initial pleural fluid findings. If none of the poor prognostic indicators were present, no invasive procedures are indicated if the patient is doing well clinically. If any of the poor prognostic indicators were present at the initial thoracentesis, a second therapeutic thoracentesis should be performed and the pleural fluid should be re-analyzed. If the pleural fluid accumulates a third time, a small 8 - 13 French chest tube should be inserted into the pleural space unless none of the poor prognostic factors (Table 2) were present at the time of the second thoracentesis.

Loculated Pleural Fluid: If the pleural fluid cannot be removed completely with a therapeutic thoracentesis or with a small chest tube, it is probably loculated. The loculation indicates a high level of inflammation in the pleural space. The majority of loculated pleural effusions require drainage. If the pleural fluid is loculated and if any of the poor prognostic factors listed in Table 1 are present, efforts should be made to break down the loculations in order to obtain complete drainage of the pleural space.

Loculations may be broken down chemically by the intrapleural injection of fibrinolytics or physically with thoracoscopy. There have been multiple uncontrolled studies which have reported high success rates with the intrapleural administration of either streptokinase12-15 or urokinase12,15,16. The usual dose of urokinase is 100,000 IU while that for streptokinase is 250,000 IU. Each agent is diluted with normal saline to a total volume of 50 - 100 ml and given daily. Urokinase is no longer available in the United States.

There have been three randomized controlled studies comparing the therapeutic efficacy of intrapleural fibrinolytics with saline. In the first study Davies and associates17 compared streptokinase with saline in a randomized double blind study. In this study the streptokinase group tended to do better, although the numbers were small and the differences did not reach statistical significance. Bouros and associates compared urokinase with saline in a randomized double blind study of 31 patients and reported that the patients receiving urokinase did significantly better in regards to the need for additional treatment18. Recently, Tuncozgur and associates randomized 49 patients to urokinase or normal saline and reported that the patients who received urokinase had significantly shorter duration of fever, lower percentage of decortication and shorter duration of hospitalization19. At the present time there is an ongoing multi-center study in the United Kingdom comparing streptokinase with saline. Since this study will have 400 patients upon its completion, it will probably be the definitive study on the efficacy of fibrinolytics for the treatment of loculated parapneumonic effusions.

The alternative approach to the patient with loculated pleural effusions is thoracoscopy with the breakdown of adhesions. In recent years there have been several uncontrolled studies purporting to show the utility of this approach20-24. One advantage of this procedure is that the chest tube can be positioned in the most dependent part of the empyema cavity. Before thoracoscopy is performed, a CT scan should be obtained. This examination will provide information about the size and extent of the empyema cavity that will guide the planned procedure. A thickened visceral pleural peel without septations suggests that the empyema may be chronic and probably will not be amenable to thoracoscopic debridement alone25.

When faced with a patient with a loculated parapneumonic effusion, should fibrinolytics be administered intrapleurally or should thoracoscopy be performed? In one study, 20 patients with loculated parapneumonic effusions were randomized to receive chest tubes with streptokinase or thoracoscopy26. The patients in the thoracoscopy group had a significantly higher primary treatment success, and a shorter duration of chest tube drainage and hospitalization. The patients in the fibrinolytic group who failed were subsequently treated successfully with thoracoscopy. Based on this study, it is recommended that patients with loculated parapneumonic effusions and poor prognostic indicators in the pleural fluid be treated initially with thoracoscopy if the expertise for this procedure is available locally. At thoracoscopy the fibrin membranes are broken down and the chest tube is placed optimally. If the lung does not expand, then attempts to perform a decortication via thoracoscopy are indicated. If the lung does not expand during thoracoscopy, then a thoracotomy with decortication is indicated. If the expertise for thoracoscopy is not available locally, then a trial of fibrinolytics is warranted. If there is not substantial improvement with the fibrinolytics within a few days, one should proceed to more invasive procedures.

Thoracotomy with Decortication: This is the most invasive procedure for the treatment of parapneumonic effusions and empyema. With decortication all the fibrous tissue is removed from the visceral pleura and all pus is evacuated from the pleural space. The primary indication for decortication is a trapped lung; loculations are better treated with thoracoscopy.

In summary, for the treatment of parapneumonic effusions and empyema one uses progressively invasive treatments if the previous treatment is not successful within a matter of days. Initially, a therapeutic thoracentesis is done to provide fluid for analysis and to remove all the fluid. For recurring pleural effusion, repeat therapeutic thoracentesis or tube thoracostomy is indicated if poor prognostic indicators (Table 2) were present at the time of the original thoracentesis. If the fluid cannot be removed due to loculations, one proceeds to intrapleural fibrinolytics or thoracoscopy. If one selects intrapleural fibrinolytics, thoracoscopy should be performed if the fibrinolytics are not successful within a few days. If the lung does not expand at thoracoscopy, one should proceed to decortication. The primary mistake in the management of patients with complicated parapneumonic effusions and empyema is that one progresses from one therapy to another too slowly. A definitive procedure should be done within 10-14 days after the patient is initially seen. A recent article from Canada demonstrates how much delay still occurs in certain regions. In this study of 34 patients from Regina General Hospital in Regina, Saskatchewan, the mean time from admission to thoracic surgery referral was 47 days and the mean number of CT scans was more than 1027.

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